RU2747004C1 - Method for producing an electrical insulation coating on metal - Google Patents

Abstract

FIELD: power electronics.

SUBSTANCE: invention relates to methods for producing electrical insulation coatings on metal substrates when producing power hybrid integrated circuits (hereinafter – PHIC) for power electronics devices. Producing of an electrical insulation coating includes preparation of a metal substrate, application of an electrical insulation metal layer, etching of the substrate with an aqueous solution of alkali and chemical polishing with a mixture of mineral acids. Then, a layer of aluminum oxide with a thickness of 45 to 55 mcm is formed on a metal substrate of an aluminum base by porous anodizing on a plant for growing aluminum oxide layers in an aqueous solution of oxalic acid with a concentration of at least 5% in galvanostatic mode at a solution temperature of 15 to 17ºC, using certain materials and parameters.

EFFECT: invention provides an improvement in dielectric characteristics of aluminum oxide layer, which is the main functional non-conductive layer on an aluminum base, which is a structure base for PHIC.

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Description

The proposed invention relates to the field of electronics, in particular to methods of obtaining electrical insulating coatings on metal substrates in the manufacture of power hybrid integrated circuits (SGIS) for power electronics devices.

The relevance of the technical problem to be solved in the development of the proposed method is based on the need to improve the dielectric properties of the aluminum oxide layer, which is the main functional non-conductive layer on an aluminum base, which is the structural basis of SGIS.

The presence of a characteristic porous structure in aluminum oxide contributes to a decrease in the electrophysical properties due to possible contamination of the pores, in particular by electrolyte residues, as well as penetration of metals into the pores during vacuum deposition of metal films. The application of the pore sealing method leads to an increase in the dielectric properties of the alumina layer.

From the prior art, a method is known for producing an electrical insulating coating on metal, glass fabric, asbestos, mica materials, which is a composition based on siloxane rubber, organophosphoric acid organoester, organic solvent and organic peroxide (RF patent No. 2011233, IPC Н01В 19/00, publ. 15.04. 1994), providing, in contrast to the previous analogue, an improvement in thermal stability, electrical insulating and physical and mechanical properties of the material.

The disadvantages of this method include insufficiently high quality of the dielectric layer, which in practice turns out to be critical, dictating specific requirements for the coating material.

The task of the authors of the present invention is to develop an effective method for obtaining a reliable electrical insulating coating on a metal, namely on aluminum, covered with a layer of aluminum oxide, which is the structural basis of SGIS.

A new technical result achieved when using the proposed method consists in improving the quality and reliability of the electrical insulating coating by stabilizing the electrical parameters of the electrical insulating coating.

The specified task and the new technical result are provided by the fact that, in contrast to the known method for producing an electrical insulating coating, including the preparation of a metal substrate, applying a layer of an electrical insulating material, according to the proposed method, the metal substrate is preliminarily prepared by etching it with an aqueous solution of alkali and chemical polishing with a mixture of mineral acids, Then, on a metal substrate, which is taken as an aluminum base, a layer of aluminum oxide with a thickness of 45% in an aqueous solution of oxalic acid with a concentration of at least 5% in a galvanostatic mode at a solution temperature of 15 to 17 ° C is preliminarily formed by the method of porous anodizing on an installation for growing alumina layers. up to 55 μm, characterized by a nanoporous structure with pore sizes from 30 to 50 nm, then an additional layer of polymer material in the form of a photoresist based on a phenolph solution is applied to this formed layer by direct pouring formaldehyde resins in dioxane, for which the aluminum base is placed in a vacuum box for 40 minutes to fill the pores of the layer of aluminum oxide with the mentioned polymer material and hardening is carried out in a drying cabinet in a stepwise mode, in the first stage of which the aluminum base with the applied layers is kept at a temperature not exceeding 90 ° C for 30 minutes, then successively at temperatures of at least 120, 150, 180 ° C, respectively, at each stage, followed by cooling to a temperature of at least 60 ° C, and then to room temperature.

The proposed method for producing an electrical insulating coating on metal is explained as follows.

In the manufacture of hybrid integrated circuits, an important parameter is the roughness and high class of surface cleanliness (12-14 class) of aluminum bases.

Due to the specifics of the anodizing process, the use of known methods, such as electropolishing, mechanical polishing, and rolling using precision shafts, do not allow achieving such a high class of base surface cleanliness, and as a result, the low quality of the resulting dielectric layer.

After a number of studies, the chemical preparation of the surface of aluminum bases was carried out in two stages:

- etching of the surface layer in an aqueous solution of sodium hydroxide (removal of various defects and contaminants from the surface of the bases resulting from mechanical processing);

- chemical polishing of the surface in a mixture of nitric and orthophosphoric acids.

As a result of the work carried out to study the chemical surface treatment, bases of the 8th grade of purity were obtained.

The dielectric strength of porous oxides is very low in the direction of the pores and increases little with increasing oxide thickness. In this regard, it becomes necessary to use special methods for increasing the dielectric strength and reducing the leakage currents of a thick-layer oxide used as a dielectric layer of aluminum bases. In this regard, the possibility of compaction (impregnation) of pores with organic material was investigated, in the quality of which the material proposed in the claimed method proved to be the most effective - positive photoresist FP-2550.

Positive photoresist FP-2550 is traditionally used in photolithography as a photosensitive intermediate material and is characterized by a number of advantages (stable insulation resistance during operation, sufficient mechanical strength of the coating on substrates made of various materials, the ability to high-quality curing after heat treatment), but the material's ability to deep penetration into the pores of the porous alumina sublayer was revealed only in the process of experimental testing of the conditions of the proposed method.

Initially, when implementing the proposed method, the aluminum bases are cleaned. Then, a nanoporous aluminum oxide layer is formed on the aluminum substrates. It has been experimentally established that the most effective material for densification (impregnation) of pores was shown by the positive photoresist FP-2550 proposed in the claimed method. A layer of FP-2550 photoresist is applied to the formed aluminum oxide layer.

Next, aluminum bases with a formed alumina layer and an applied photoresist layer are placed in a vacuum box for 40 minutes to fill the pores of the dielectric layer with organic material (photoresist, which is a complex organic compound). After the process of forced impregnation of solid porous aluminum oxide with a liquid photoresist, a stepwise hardening of the photoresist is carried out in the pores of the dielectric layer at the first stage of which the aluminum base is kept at a temperature of no more than 90 ° C for 30 minutes, then sequentially at temperatures of at least 120, 150, 180 ° C respectively, at each stage, followed by cooling to a temperature of at least 60 ° C, and then to room temperature.

To check the electrophysical properties of thick-layer oxide, a contact mask "vanadium-copper" with a thickness of 2.6 to 2.8 microns is sprayed onto the aluminum bases with deposited layers, and contact metal pads are formed by photolithography.

FIG. 1 shows the surface of a sample with formed contact areas, where 1 is a voltage electrode, 2 is a measuring electrode, 3 is a dielectric.

FIG. 2 shows the surface of a sample with formed contact areas in section, where 1 is a voltage electrode, 2 is a measuring electrode, 3 is a dielectric.

In the process of experimental development of the proposed method for filling the pores of thick-layer aluminum oxide with a positive photoresist FP-2550, it was possible to achieve a significant improvement and stability of the electrophysical parameters of the dielectric layer of aluminum oxide.

Thus, when implementing the proposed method, the quality and reliability of the electrical insulating coating on an aluminum base is improved by stabilizing the electrophysical parameters of the electrical insulating coating.

The possibility of industrial implementation of the proposed method is confirmed by the following example of a specific implementation. Example 1.

In laboratory conditions, the claimed method was tested using aluminum bases made of an AD1M alloy with a size of 48 × 60 × 1.5 mm (GOST 13726-97). First, a two-stage chemical preparation of the surface of aluminum substrates is carried out. At the first stage, various defects and contaminants are removed from the surface of the bases, obtained as a result of mechanical treatment by etching the surface layer in an aqueous solution of sodium hydroxide. At the second stage, the surface is chemically polished in the mixture by cooling to a temperature of at least 60 ° C, and then to room temperature. To check the electrophysical properties of a thick-layer oxide, a contact mask "vanadium-copper" with a thickness of 2.6 to 2.8 microns is sprayed onto the samples. Contact metal pads are formed on the samples by photolithography. To assess the quality of filling the pores of the dielectric layer, the dielectric properties of thick-layer aluminum oxide were studied. The research results are summarized in Table 1.

Claims (1)

A method for producing an electrical insulating coating on a metal, including preparing a metal substrate, applying a layer of an electrical insulating material, characterized in that the metal substrate is preliminarily prepared by etching with an aqueous solution of alkali and chemical polishing with a mixture of mineral acids, then on the metal substrate, which is taken as an aluminum base, is formed by the method of porous anodizing on an installation for growing alumina layers in an aqueous solution of oxalic acid with a concentration of at least 5% in a galvanostatic mode at a solution temperature of 15 to 17 ° C a layer of aluminum oxide with a thickness of 45 to 55 μm, characterized by a nanoporous structure with pore sizes from 30 to 50 nm, then a layer of polymeric material in the form of a photoresist based on a solution of phenol-formaldehyde resins in dioxane is additionally applied to this formed layer by direct pouring, for which the aluminum base with the formed layers is placed in a vacuum b ox for 40 minutes to fill the pores of the main electrical insulating layer of aluminum oxide with the mentioned polymeric material and hardening is carried out in an oven in a stepwise mode, in the first stage of which the aluminum base is kept at a temperature of no more than 90 ° C for 30 minutes, then sequentially at temperatures not less than 120, 150, 180 ° C, respectively, at each stage, followed by cooling to a temperature of at least 60 ° C, and then to room temperature.

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